Shotgun cartridges fall into two broad yet distinct categories. The first category includes designs which launch dense-metal bullets or projectiles at velocities typically greater than 300 meters-per-second. The second category consists of designs which launch lower-density bullets, projectiles, and aggregate filled bags at velocities typically lower than 150 meters-per-second. Cartridge design optimizes launch velocity within a category to maximize the desired terminal effects, namely, lethal penetration at high velocity and non-lethal impact at low velocity. Single-velocity cartridge designs severely limit the utility of ammunition. More importantly, single-velocity designs fix the response level of the user irrespective of the threat or situation.
Adjustable velocity ammunition is confined to large caliber shells. These inventions include rigidly-attached, segmented propellant beds and various selection mechanisms.
Grandy U.S. Pat. No. 3,283,719, 1966 describes a multi-bed propellant chamber to achieve multi-range capability irrespective of gun barrel length. A plurality of independent propellant charges are arranged in eccentric beds with respect to the longitudinal axis of the shell. The effective range of the projectile is increased by increasing the number of charges ignited. This design suffers four deficiencies. First, the eccentric arrangement of propellant charges produces an asymmetric pressure field which promotes damage to the projectile. Second, a plurality of primers are required to ignite the several propellant charges thereby making the design incompatible with single-point, centered firing pins employed in conventional gun systems. Third, the disc used to shield non-initiated propellant beds from the ignited charge is likely to remain in the gun barrel thereby interfering with the firing cycle. And fourth, noninitiated propellant charges are susceptible to temperature buildup leading to its undesired ignition. This problem is pronounced where the propellant bed, shell case, and gun breach are in close proximity. This deficiency precludes application of Grandy type devices to weapons with high rates of fire where the gun breach is subjected to extreme temperature elevations.
Romer U.S. Pat. No. 4,619,202, 1986 describes another multi-bed propellant chamber which achieves multi-range capability. Two or more independent circular propellant charges are arranged coaxially with respect to the longitudinal axis of the shell casing. Mechanical initiation of the lower most propellant bed is achieved by a firing pin. Electrical initiation via an electronics circuit allows for selective ignition of a plurality of propellant beds thus achieving the desired velocity. Propellant beds are mechanically secured in series with the base of the projectile. This invention suffers from three deficiencies. First, the coaxial arrangement and construction of the propellant beds is prone to generating debris which in turn enters the gun barrel thereby interfering with the firing cycle. Second, attachment of the propellant beds to the projectile to facilitate the transport of the non-initiated beds from the gun barrel adds parasitic mass and alters the aerodynamic characteristics of the projectile. Both events adversely impact projectile performance in terms of reduced range and altered flight dynamics. And third, reliance on an electronic ignition circuit to achieve selectability precludes use in conventional handguns, shotguns, and rifles which employ a mechanical firing pin.
As is apparent from the inventions above, neither facilitates the following: a mechanically-based selector mechanism housed within a sealed cartridge; a selector mechanism based on a rotatable multi-chamber propellant bed; a selector mechanism compatible with single-pin firing systems and based on a single, mechanically initiated primer; and a selector design and propellant bed arrangement which result in the debris free ignition of a single propellant bed.
It is therefore the primary object of this invention to provide a selectable cartridge that:
A. Provides the mechanical selection of one of two propellant beds thereby facilitating either a low-velocity or a high-velocity launch.
B. Incorporates a single primer system compatible with conventional firing pins.
C. Incorporates a coaxial bed arrangement in which a low-velocity bed and a high-velocity bed are contained in a single unit operating in a debris-free fashion.
D. Incorporates a propellant bed arrangement in which a thermally insulated high-velocity bed remains in the cartridge after discharge of the low-velocity bed.
E. Incorporates a propellant bed arrangement which is launched with the projectile from the barrel when the high-velocity bed is discharge thereby functioning as the wad in a conventional shotgun round and expelling the non-initiated propellant contained in the low-velocity bed.
F. Maintains the optimum flight characteristics of the projectile.